Pattern Evaluation Method

ABSTRACT

In a pattern evaluation method of determining whether a pattern formed on a photomask is acceptable, an aberration parameter of an image quality evaluation apparatus for determining a pattern image intensity in transferring a pattern formed on a photomask onto a wafer is acquired. An acceptance criterion value used in determining whether an abnormal pattern of the photomask including the effect of aberration of the image quality evaluation apparatus is acceptable is set through a lithographic simulation using the acquired aberration parameter. Then, using the image quality evaluation apparatus, an image intensity of the abnormal pattern of the photomask and an image intensity of a normal pattern corresponding to the abnormal pattern are obtained. It is determined whether the difference between the two acquired image intensities is within the set acceptance criterion value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2007-263690, filed Oct. 9, 2007,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates a pattern evaluation method for defective partsor corrected parts of a photomask, and more particularly to a patternevaluation method using an image quality evaluation apparatus which hasthe same-wavelength light source and the same optical system as those ofan exposure device used for wafer transfer.

2. Description of the Related Art

One known photomask pattern evaluation method is to evaluate the effectof an abnormal part including a defective pattern of a photomask inwafer transfer. Such a pattern evaluation method is used mainly in theprocess of correcting a defective part of a photomask. In the method, animage quality evaluation apparatus is used. The image quality evaluationapparatus, which has the same-wavelength light source and the sameoptical system as those of an exposure device, images and analyzes awafer transfer image as an Aerial Image Measurement System (AIMS),produced by Carl Zeiss, Inc., does.

To evaluate a pattern, the image of an abnormal part, such as a defectin a wafer transfer pattern image or a defect-corrected part is imagedwith an image quality evaluation apparatus. On the basis of the image ofan abnormal part and the image of a normal part corresponding to theabnormal part (the part obtaining by removing the defects from theabnormal part, or another part whose pattern layout approximates to thepart obtained by removing the defects from the abnormal part), a lightintensity distribution of the abnormal part is compared with that of thenormal part, thereby calculating the variation in, for example, thetransmittance of the abnormal part and the dimensions to be transferredto the wafer with respect to the normal part. Then, the pattern isevaluated by determining whether the variations are within an allowablerange in a wafer lithographic process.

In such an evaluation method, it is desirable that the image obtained bythe image quality evaluation apparatus should coincide completely with aspatial image actually reaching the wafer surface. For various reasons,however, the former actually differs slightly from the latter. One greatfactor for this is the aberration of the optical system of theapparatus. When the pattern of an abnormal part is evaluated with theimage quality evaluation apparatus, measurements are made automatically,including errors caused by the aberration. Since the aberration of thequality evaluation apparatus acting as an inspection apparatus isrelatively small, the aberration has caused little trouble.

However, as patterns have been miniaturized further, the effect ofaberration has increased, which makes pattern evaluation more difficult.To reduce the aberration, the body of the apparatus has to be improved.The only way to achieve this is either to increase the performance ofeach of the lenses or to adjust the aberration correction mechanism in asuitable way. However, the aberration cannot be made so small that itseffect can be ignored. Depending on the photomask pattern, the effect ofthe aberration can appear significantly.

Dominant aberrations in evaluating patterns with the image qualityevaluation apparatus include coma aberration and astigmatism.Astigmatism causes a phenomenon where the horizontal light condensingposition of the optical system differs from the vertical one, resultingin a decrease in the measurement accuracy of the mask pattern. It issaid that coma aberration is observed as a result of the disruption ofthe balance of the sub-peak at the mask pattern edge part. Thedisruption of the balance is caused by a phenomenon where light does notconverge at a point on an imaging surface and forms a fan-like image insuch a manner that light leaves traces. The effect of the aberrationsmakes the light intensity distribution asymmetrical in a part where, forexample, a densely arranged pattern part is close to a roughly arrangedpattern part, which makes pattern evaluation difficult.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided a patternevaluation method comprising: acquiring an aberration parameter of animage quality evaluation apparatus for determining a pattern imageintensity in transferring a pattern formed on a photomask onto a wafer;setting an acceptance criterion value used in determining whether anabnormal pattern of the photomask including the effect of aberration ofthe image quality evaluation apparatus is acceptable, through alithographic simulation using the acquired aberration parameter;acquiring an image intensity of the abnormal pattern of the photomaskand an image intensity of a normal pattern corresponding to the abnormalpattern with the image quality evaluation apparatus; and determiningwhether the difference between the two acquired image intensities iswithin the set acceptance criterion value.

According to another aspect of the invention, there is provided aphotomask manufacturing method comprising: acquiring an aberrationparameter of an image quality evaluation apparatus for determining apattern image intensity in transferring a pattern formed on a photomaskonto a wafer; setting an acceptance criterion value used in determiningwhether an abnormal pattern of the photomask including the effect ofaberration of the image quality evaluation apparatus is acceptable,through a lithographic simulation using the acquired aberrationparameter; acquiring an image intensity of the abnormal pattern of thephotomask and an image intensity of a normal pattern corresponding tothe abnormal pattern with the image quality evaluation apparatus;determining whether the difference between the two acquired imageintensities is within the set acceptance criterion value; and correctingthe abnormal pattern determined not to be within the acceptancecriterion value.

According to still another aspect of the invention, there is provided asemiconductor device manufacturing method comprising: acquiring anaberration parameter of an image quality evaluation apparatus fordetermining a pattern image intensity in transferring a pattern formedon a photomask onto a wafer; setting an acceptance criterion value usedin determining whether an abnormal pattern of the photomask includingthe effect of aberration of the image quality evaluation apparatus isacceptable, through a lithographic simulation using the acquiredaberration parameter; acquiring an image intensity of the abnormalpattern of the photomask and an image intensity of a normal patterncorresponding to the abnormal pattern with the image quality evaluationapparatus; determining whether the difference between the two acquiredimage intensities is within the set acceptance criterion value;correcting the abnormal pattern determined not to be within theacceptance criterion value; and transferring a pattern onto a specimenusing a photomask subjected to the pattern correction.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a schematic diagram showing a photomask pattern for evaluationaccording to an embodiment of the invention;

FIG. 2 is a flowchart to help explain a pattern evaluation methodaccording to the embodiment;

FIG. 3 is a light intensity profile plot calculated using a lithographicsimulation along line A of FIG. 1;

FIG. 4 is a light intensity profile plot measured along line A of FIG. 1with an image quality evaluation apparatus;

FIG. 5 is a schematic diagram of a hole pattern used for measuringastigmatism;

FIG. 6 is a graph obtained by plotting a defocus characteristic ofcontrast in each of the vertical and horizontal directions shown by thearrows in FIG. 5;

FIG. 7 is a schematic diagram of a hole pattern used for measuring comaaberration;

FIG. 8 is a light intensity profile plot calculated using a lithographicsimulation along line B of FIG. 7;

FIG. 9 is a light intensity profile plot measured along line B of FIG. 7with the image quality evaluation apparatus;

FIG. 10 is a schematic diagram showing a mask pattern with a residualdefect in FIG. 1;

FIG. 11 is a schematic diagram showing a mask pattern with a chippeddefect in FIG. 1;

FIG. 12 is a graph obtained by plotting errors of a defect with respectto the size of a residual defect of FIG. 10; and

FIG. 13 is a graph obtained by plotting errors in a defect with respectto the size of a chipped defect of FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, referring to the accompanying drawings, an embodiment ofthe invention will be explained in detail.

Embodiment

First, as shown in FIG. 1, a mask on which a line-and-space pattern hasbeen made of a light-shielding film 12 is prepared on a quartz (Qz)substrate 11 as a photomask. A defect (which denotes a part whose shapediffers from a desired pattern in the design data or drawing data on thephotomask and is the same as an abnormal part) in the mask is detectedand position information on the defect and defect image data areacquired with a mask defect inspection apparatus. On the basis of thesepieces of information, an abnormal part including a defect is evaluatedwith an image quality evaluation apparatus which has a light sourcewhose wavelength is the same as that of an exposure device and the sameoptical system (NA, σ, lighting condition) as that of the exposuredevice. Then, it is determined whether the effect on wafer transfer, theeffect of the aberration of the apparatus, can be ignored. The detailsof the procedure will be explained with reference to a flowchart in FIG.2.

The mask is put in the image quality evaluation apparatus andmeasurement conditions are set so as to be the same as the exposureconditions for wafer transfer. After a suitable rotation correction ismade, the image quality evaluation apparatus is moved to a mask defectposition previously obtained from the defect inspection apparatus.Thereafter, a pattern image for wafer transfer is imaged with a squarevisual field, about 10 μm on a side, centering on the defect (step S1).The size of the image can be set to the size of the necessary areaaccording to the mask pattern. Similarly, the image of a normal patterncorresponding to the abnormal pattern in the abnormal part is imaged anda light intensity profile plot corresponding to line A of FIG. 1 in eachof the abnormal part and normal part is obtained. At this time, if anormal pattern exists in the image of the abnormal part, a lightintensity profile plot of the normal pattern can be obtained from theimage of the abnormal part. Therefore, the pattern of the normal partmay not be imaged again. That is, when the light intensity profile plotof the pattern in the normal part corresponding to the abnormal part canbe estimated from the light intensity distribution of the normal patternfree from defects in the image of the abnormal part, the imaging of thepattern of the normal part may be omitted.

The reason why the normal pattern is subjected to a lithographicsimulation is that it is difficult to evaluate an abnormal pattern usinga lithographic simulation. The reason is further that an abnormalpattern differs from a pattern of design data and an abnormal partdevelops accidentally.

Here, the light intensity profile plot obtained with the image qualityevaluation apparatus is not an ideal light intensity profile plotcalculated using a simulation as shown in FIG. 3 and is affected by theaberration of the image quality evaluation apparatus as shown in FIG. 4.Since the light intensity distribution differs from an ideal one, it isdifficult to evaluate the patterns accurately. To overcome this problem,the amount of aberration of the image quality evaluation apparatus isdetermined using a lithographic simulation (step S2).

First, the parameter for an astigmatism value is obtained. Sinceastigmatism is caused by the difference between the vertical focusposition and the horizontal focus position, the astigmatism value isobtained using a hole pattern that enables the vertical and horizontalfocus positions to be measured at the same time. With a mask having asquare hole pattern, 0.5 to 1 μm on a side, as shown in FIG. 5, aplurality of points are imaged in defocus by the image qualityevaluation apparatus. The vertical contrast and horizontal contrast asshown by arrows A and B in FIG. 5 are analyzed and a defocuscharacteristic is plotted as in FIG. 6. In FIG. 6, the place where thecontrast is the highest is a focus position. The difference between thevertical focus position and the horizontal focus position is calculated.The difference of the focus position on the image surface results fromastigmatism. The calculated difference is the amount of astigmatism ofthe image quality evaluation apparatus.

Under the same measuring condition as that for obtaining the astigmatismvalue using the hole pattern of FIG. 5, a spatial image is calculatedusing a lithographic simulation. In a calculation taking no account ofaberration, there is no shift in the focus position. When the parametercorresponding to the astigmatism in the lithographic simulation ischanged, the difference between the vertical focus position and thehorizontal focus position occurs. The parameter is changed in such amanner that the difference becomes equal to the measured amount ofastigmatism of the image quality evaluation apparatus. The parametervalue at a position where the difference coincides with the measuredvalue is found. At this time, the terms related to astigmatism such asthe fifth and sixth terms in a Zernike polynomial, are used asparameters. By the method, the value of astigmatism of the image qualityevaluation apparatus is quantified using a simulation and this value isused as Asti.

Next, to calculate the coma aberration of the image quality evaluationapparatus, an image is imaged by the image quality apparatus using amask pattern which enables coma aberration to be calculated with such arelatively simple structure as a square hole pattern, 4 to 5 μm on aside, shown in FIG. 7. Then, the light intensity profile plotscorresponding to line C and line D of FIG. 7 are obtained. Line C isused to calculate a coma aberration value affecting the horizontaldirection and line D is used to calculate a coma aberration valueaffecting the vertical direction.

As a result of coma aberration, the peaks 13, 14 at the edge parts ofthe light intensity profile plot along line C have a left-rightasymmetrical shape as shown in FIG. 8. The difference between theindividual peak heights is calculated. Then, using a lithographicsimulation, a spatial image of a similar hole pattern is calculated. Ifcalculations are done without giving a coma aberration value, the leftand right peaks of the light intensity profile plot obtained as in FIG.9 coincide with each other.

The 7th, 14th, 23rd, and 34th terms in a Zernike polynomial are used asthe parameters related to coma aberration. In addition to these, thereare the 8th, 15th, 24th, and 35th terms in the Zernike polynomial as theparameters related to coma aberration. However, they are not used herebecause they affect the vertical light intensity distribution. A changein the light intensity distribution caused by each of the parameters ofthe 7th, 14th, 23rd, and 34th terms is calculated. On the basis of theresult, the value of the 7th term is changed so as to make almost thesame difference as the measured value. If the measured value (FIG. 8)does not coincide with the peak of the simulation value using only thevalue of the 7th term, the value of each of the 14th, 23rd, and 34thterms is changed in that order so that the peak differences and shapesmeasured with the image quality evaluation apparatus may coincide withone another. Let the parameter values obtained here be Coma-X.

In the light intensity profile plot along line D in the verticaldirection, too, a coma aberration value is determined in the same mannerusing a lithographic simulation. In this case, the parameters used arethe 8th, 15th, 24th, and 35th terms in the Zernike polynomial. Let theparameter values obtained here be Coma-Y.

On the basis of the aberration parameters obtained by the above method,a final adjustment of the aberration value is made according to apattern to be evaluated.

First, using the pattern of FIG. 1, a spatial image is calculated usinga lithographic simulation under the same exposure condition as that forthe measurement of the image quality evaluation apparatus, therebyobtaining a light intensity profile plot shown in FIG. 4. The aberrationparameters Asti, Coma-X, and Coma-Y are input to make calculations. Ifthe obtained light intensity profile plot does not coincide with thelight intensity profile plot of the actual measurement values of FIG. 4,the aberration parameters are newly changed slightly to make a fineadjustment. Then, the finally obtained aberration value is used asaberration parameter X.

The value of aberration parameter X differs, depending on the exposureconditions (NA, sigma aperture, pupil shape) or the type of pattern.Therefore, the aberration values have to be adjusted for each of theexposure conditions and mask patterns on the basis of the aberrationvalues obtained using the basic exposure conditions, including as Asti,Coma-X, and Coma-Y, and the type of pattern.

Next, using aberration parameter X, an acceptance criterion value forpattern evaluation is set (step S3).

On the basis of a defect image on the mask defect inspection apparatusor an image under a scanning electron microscope (SEM), the shape of adefect in an abnormal part is extracted. Then, it is determined whetherthe extracted defect is a residual defect caused as a result of anunnecessary light-shielding film remaining in a place not shown in themask drawing data or a chipped defect caused as a result of alight-shielding film getting chipped. FIG. 10 shows a state where aresidual defect 15 has occurred and FIG. 11 shows a state where achipped defect 16 has occurred. Moreover, the defect size is measuredroughly to determine how large the defect is for the pattern.

First, when a defect is a residual defect 15 as shown in FIG. 10, therange of errors in the defective part for a wafer transfer image iscalculated using a simulation. FIG. 10 shows a structure where theline-and-space pattern 12 of FIG. 1 is arranged. A residual defect 15has occurred in the pattern 12. A light intensity profile plot alongline E of FIG. 10 is observed. Thereafter, the size of the defect alongline E is changed according to the pattern size of the mask. An error iscalculated for a plurality of sizes using a lithographic simulation. Thetendency of the degree of effect of the defect is shown in graph form.

As for errors, a change in the pattern dimensions after the wafertransfer of an abnormal part compared with a normal part is determinedusing the following expression:

|the dimensions of a normal part−the dimensions of a defective part|/thedimensions of the normal part×100(%)  (1)

The graph of FIG. 12 is obtained by finding changes in the patterndimensions after wafer transfer caused by a defect as shown in FIG. 10and plotting a difference from the normal part for the size of thedefect. In a defect error evaluation method, the evaluation point maydiffer according to the position of a defect or the pattern shape.Alternatively, a method of evaluating the difference of patterndimensions or the relative difference of transmittance may be used. Fromthe graph of FIG. 12, the threshold value (Def-s1) of a defect size isdetermined which meets an acceptance criterion value 1 (mark-S1) set asa range in which the effect of a defect in a photomask pattern on actualwafer transfer can be ignored.

Next, under the conditions including aberration parameter X, an errorcaused by the residual defect 15 is calculated. The tendency of thedegree of effect of the defect is shown in graph form (a dotted line inFIG. 12). At this time, the comparison with the actual measurement valueof the image quality evaluation apparatus including the effect ofaberration is made at several points, making it possible to consider theeffect of aberration more accurately, which improves the patternevaluation accuracy. In a state where the aberration parameter isincluded, let acceptance criterion value 2 corresponding to Def-s1 bemark-A.

Next, when a chipped defect 16 as shown in FIG. 11 is arranged on thesame pattern as the one on which the defect of FIG. 10 is arranged, anacceptance criterion value 2 taking the effect of aberration intoaccount is set.

The chipped defect 16 as shown in FIG. 11 is calculated by the samemethod using a simulation and the degree of effect of the defect isshown in graph form (FIG. 13). A solid line in FIG. 13 shows the degreeof effect on the condition that there is no aberration. A dotted lineshows the degree of effect on the condition that aberration values areincluded. From the graph of FIG. 13, the threshold value (Def-s2) of adefect size is determined which meets an acceptance criterion value 2(mark-S2) set as a range in which the effect of a defect on wafertransfer can be ignored. In a state where the aberration parameter isincluded, let acceptance criterion value 2 corresponding to Def-s2 bemark-B.

When an acceptance criterion value is set, any one of the acceptancecriterion values 1 and 2 may be used according to the type or positionof a defect, the size of a mask pattern, dimensions, or shape. Theacceptance criterion value 1 is a criterion value of the degree ofeffect of a defect for a spatial image when there is no aberration and apattern is transferred ideally onto a wafer. The acceptance criterionvalue 2 is a criterion value of the degree of effect of a defect for aspatial image including the aberration value of the image qualityevaluation apparatus. For example, an error in the defect of FIG. 10 isaffected by the aberration and is under condition mark-A stricter thanthe acceptance criterion value mark-S1 in ideal wafer transfer as shownin FIG. 12. However, an error in the defect of FIG. 11 is undercondition mark-B less strict than mark-S2 as shown in FIG. 13. Asdescribed above, the setting of the acceptance criterion value 2 notonly makes the criterion value stricter, taking the effect of aberrationinto account, but also optimizes the value according to the type orposition of a defect or the position of a pattern.

In this way, an acceptance criterion value including the effect ofaberration of the image quality evaluation apparatus can be set. Next,an abnormal pattern including a defect in the photomask is evaluatedwith the image quality evaluation apparatus.

As in step S1 explained above, on the basis of position information on adefect acquired from the defect inspection apparatus, a square maskarea, about 10 μm on a side, including a defect is imaged with the imagequality evaluation apparatus, thereby obtaining an image intensity of anabnormal part. If there are a plurality of defects, an image intensityis obtained for each of all the defects. The following admissiondecision is made on all of the defects.

On the basis of the light intensity distribution of the defective partof the abnormal part acquired from the image quality evaluationapparatus, a change (error) in the dimensions of the defective part withrespect to the normal part after wafer transfer is calculated usingexpression (1) described above. On the basis of acceptance criterionvalue 2 (mark-A or mark-B) obtained by the above method, it isdetermined whether an error caused by a defect is acceptable (step S4).If the error exceeds acceptance criterion value 2 and the defect in theabnormal part has to be corrected, the defect is corrected by a maskdefect correction unit. Thereafter, the defect-corrected part ismeasured again with the image quality evaluation apparatus and it isdetermined on the basis of acceptance criterion value 2 (mark-A ormark-B) whether the defect is within an error range.

As described above, the aberration of the image quality evaluationapparatus is obtained and an acceptance criterion value is set through alithographic simulation using the aberration, which makes it possible toreduce a measurement error caused by the aberration of the image qualityevaluation apparatus. Accordingly, the accuracy of pattern evaluation bythe image quality evaluation apparatus can be improved.

Moreover, a strict acceptance criterion value including an error in theaberration of the apparatus is not set and additional work of correctingeven a part where the effect of a detect on pattern transfer is withinan allowable error range can be omitted.

Furthermore, using a mask determined to be acceptable by such anevaluation method, a wafer on which surface a high-accuracy pattern hasbeen formed within an allowable error range according to the dimensions,shape, and layout set in the design stage can be obtained. Thereafter,by a well-known dicing process, mount process, banding process,packaging process, and other processes, a desired design pattern isformed on the wafer. Then, a semiconductor device including the wafer isobtained. That is, applying the invention to a semiconductor devicemanufacturing method enables a highly reliable semiconductor device tobe realized.

(Modification)

The invention is not limited to the above-described embodiment. While inthe embodiment, a transparent substrate on which a pattern of alight-shielding material has been formed is used as a photomask, theinvention is not limited to this and may be applied to a transparentsubstrate on which a translucent pattern (halftone pattern) has beenformed. Furthermore, in the process of obtaining the aberration of theimage quality evaluation apparatus, not only coma aberration andastigmatism but also other aberration parameters may be obtained at thesame time.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A pattern evaluation method comprising: acquiring an aberrationparameter of an image quality evaluation apparatus for determining apattern image intensity in transferring a pattern formed on a photomaskonto a wafer; setting an acceptance criterion value used in determiningwhether an abnormal pattern of the photomask including the effect ofaberration of the image quality evaluation apparatus is acceptable,through a lithographic simulation using the acquired aberrationparameter; acquiring an image intensity of the abnormal pattern of thephotomask and an image intensity of a normal pattern corresponding tothe abnormal pattern with the image quality evaluation apparatus; anddetermining whether the difference between the two acquired imageintensities is within the set acceptance criterion value.
 2. The patternevaluation method according to claim 1, wherein, to obtain theaberration parameter of the image quality evaluation apparatus, causingthe image quality evaluation apparatus to determine a light intensityprofile plot for a specific pattern for calculating the amount ofaberration formed on the photomask and calculating an aberrationparameter from the light intensity profile plot, causing the imagequality evaluation apparatus to determine a light intensity profile plotfor the normal pattern, and determining a light intensity profile plotfor the normal pattern using a lithographic simulation while changingthe calculated aberration parameter, and obtaining an aberrationparameter when the light intensity profile plot for the normal patternobtained using the lithographic simulation is nearest to the lightintensity profile plot for the normal pattern obtained by the imagequality evaluation apparatus.
 3. The pattern evaluation method accordingto claim 1, wherein, to set the acceptance criterion value, determininga first light intensity profile plot corresponding to the abnormalpattern using a lithographic simulation to which the aberrationparameter has not been added, determining a second light intensityprofile plot corresponding to the abnormal pattern using a lithographicsimulation to which the aberration parameter has been added, determininga first acceptance criterion value from the first light intensityprofile plot, thereby determining a threshold value of a defect size ofthe abnormal pattern, and determining a second acceptance criterionvalue corresponding to the threshold value from the second lightintensity profile plot and setting the second acceptance criterion valueas an acceptance criterion value.
 4. The pattern evaluation methodaccording to claim 3, wherein the first acceptance criterion value is avalue set as a range where the effect of a defect in the photomask onactual wafer transfer is practically ignorable under the condition thatthe aberration parameter of the image quality evaluation apparatus isignored, and the second acceptance criterion value is a value set as arange where the effect of a defect in the photomask on actual watertransfer is practically ignorable under the condition that theaberration parameter of the image quality evaluation apparatus is takeninto account.
 5. The pattern evaluation method according to claim 1,wherein the aberration includes coma aberration and astigmatism and theaberration parameter is set using a Zernike polynomial for a projectionoptical system in a lithographic simulation.
 6. The pattern evaluationmethod according to claim 1, wherein an image quality evaluationapparatus performs imaging corresponding to a wafer transfer imageobtained by transferring a pattern of the photomask onto the wafer withan exposure device and uses the same-wavelength light source and thesame optical system condition as those of the exposure device.
 7. Aphotomask manufacturing method comprising: acquiring an aberrationparameter of an image quality evaluation apparatus for determining apattern image intensity in transferring a pattern formed on a photomaskonto a wafer; setting an acceptance criterion value used in determiningwhether an abnormal pattern of the photomask including the effect ofaberration of the image quality evaluation apparatus is acceptable,through a lithographic simulation using the acquired aberrationparameter; acquiring an image intensity of the abnormal pattern of thephotomask and an image intensity of a normal pattern corresponding tothe abnormal pattern with the image quality evaluation apparatus;determining whether the difference between the two acquired imageintensities is within the set acceptance criterion value; and correctingthe abnormal pattern determined not to be within the acceptancecriterion value.
 8. The photomask manufacturing method according toclaim 7, wherein, to obtain the aberration parameter of the imagequality evaluation apparatus, causing the image quality evaluationapparatus to determine a light intensity profile plot for a specificpattern for calculating the amount of aberration formed on the photomaskand calculating an aberration parameter from the light intensity profileplot, causing the image quality evaluation apparatus to determine alight intensity profile plot for the normal pattern, and determining alight intensity profile plot for the normal pattern using a lithographicsimulation while changing the calculated aberration parameter, andobtaining an aberration parameter when the light intensity profile plotfor the normal pattern obtained using the lithographic simulation isnearest to the light intensity profile plot for the normal patternobtained by the image quality evaluation apparatus.
 9. The photomaskmanufacturing method according to claim 7, wherein, to set theacceptance criterion value, determining a first light intensity profileplot corresponding to the abnormal pattern using a lithographicsimulation to which the aberration parameter has not been added,determining a second light intensity profile plot corresponding to theabnormal pattern using a lithographic simulation to which the aberrationparameter has been added, determining a first acceptance criterion valuefrom the first light intensity profile plot, thereby determining athreshold value of a defect size of the abnormal pattern, anddetermining a second acceptance criterion value corresponding to thethreshold value from the second light intensity profile plot and settingthe second acceptance criterion value as an acceptance criterion value.10. The photomask manufacturing method according to claim 9, wherein thefirst acceptance criterion value is a value set as a range where theeffect of a defect in the photomask on actual wafer transfer ispractically ignorable under the condition that the aberration parameterof the image quality evaluation apparatus is ignored, and the secondacceptance criterion value is a value set as a range where the effect ofa defect in the photomask on actual wafer transfer is practicallyignorable under the condition that the aberration parameter of the imagequality evaluation apparatus is taken into account.
 11. The photomaskmanufacturing method according to claim 7, wherein the aberrationincludes coma aberration and astigmatism and the aberration parameter isset using a Zernike polynomial for a projection optical system in alithographic simulation.
 12. The photomask manufacturing methodaccording to claim 7, wherein the image quality evaluation apparatusperforms imaging corresponding to a wafer transfer image obtained bytransferring a pattern of the photomask onto the wafer with an exposuredevice and uses the same-wavelength light source and the same opticalsystem condition as those of the exposure device.
 13. A semiconductordevice manufacturing method comprising: acquiring an aberrationparameter of an image quality evaluation apparatus for determining apattern image intensity in transferring a pattern formed on a photomaskonto a wafer; setting an acceptance criterion value used in determiningwhether an abnormal pattern of the photomask including the effect ofaberration of the image quality evaluation apparatus is acceptable,through a lithographic simulation using the acquired aberrationparameter; acquiring an image intensity of the abnormal pattern of thephotomask and an image intensity of a normal pattern corresponding tothe abnormal pattern with the image quality evaluation apparatus;determining whether the difference between the two acquired imageintensities is within the set acceptance criterion value; correcting theabnormal pattern determined not to be within the acceptance criterionvalue; and transferring a pattern onto a specimen using a photomasksubjected to the pattern correction.
 14. The semiconductor devicemanufacturing method according to claim 13, wherein, to obtain theaberration parameter of the image quality evaluation apparatus, causingthe image quality evaluation apparatus to determine a light intensityprofile plot for a specific pattern for calculating the amount ofaberration formed on the photomask and calculating an aberrationparameter from the light intensity profile plot, causing the imagequality evaluation apparatus to determine a light intensity profile plotfor the normal pattern, and determining a light intensity profile plotfor the normal pattern using a lithographic simulation while changingthe calculated aberration parameter, and obtaining an aberrationparameter when the light intensity profile plot for the normal patternobtained using the lithographic simulation is nearest to the lightintensity profile plot for the normal pattern obtained by the imagequality evaluation apparatus.
 15. The semiconductor device manufacturingmethod according to claim 13, wherein, to set the acceptance criterionvalue, determining a first light intensity profile plot corresponding tothe abnormal pattern using a lithographic simulation to which theaberration parameter has not been added, determining a second lightintensity profile plot corresponding to the abnormal pattern using alithographic simulation to which the aberration parameter has beenadded, determining a first acceptance criterion value from the firstlight intensity profile plot, thereby determining a threshold value of adefect size of the abnormal pattern, and determining a second acceptancecriterion value corresponding to the threshold value from the secondlight intensity profile plot and setting the second acceptance criterionvalue as an acceptance criterion value.
 16. The semiconductor devicemanufacturing method according to claim 15, wherein the first acceptancecriterion value is a value set as a range where the effect of a defectin the photomask on actual wafer transfer is practically ignorable underthe condition that the aberration parameter of the image qualityevaluation apparatus is ignored, and the second acceptance criterionvalue is a value set as a range where the effect of a defect in thephotomask on actual wafer transfer is practically ignorable under thecondition that the aberration parameter of the image quality evaluationapparatus is taken into account.
 17. The semiconductor devicemanufacturing method according to claim 13, wherein the aberrationincludes coma aberration and astigmatism and the aberration parameter isset using a Zernike polynomial for a projection optical system in alithographic simulation.
 18. The semiconductor device manufacturingmethod according to claim 13, wherein the image quality evaluationapparatus performs imaging corresponding to a wafer transfer imageobtained by transferring a pattern of the photomask onto the wafer withan exposure device and uses the same-wavelength light source and thesame optical system condition as those of the exposure device.